1. Field of the Invention
The present invention relates to a spin valve read head with an antiferromagnetic oxide film as a longitudinal bias layer and a portion of the first read gap layer, and more particularly to a spin valve read head wherein a ferromagnetic free layer of a spin valve sensor is longitudinally biased by an antiferromagnetic oxide film that is located between an insulation gap layer and the spin valve sensor so as to form a portion of the first read gap.
2. Description of Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads. The read and write heads are directly fabricated on a slider that has an air bearing surface (ABS). The slider is suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to locate the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program for implementing the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A magnetic gap is formed between the first and second pole piece layers by a write gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes first and second shield layers, first and second gap layers, a read sensor and first and second lead layers that are connected to the read sensor for conducting a sense current through the read sensor. The first and second gap layers are located between the first and second shield layers and the read sensor and the first and second lead layers are located between the first and second gap layers. The distance between the first and second shield layers determines the linear read density of the read head. Accordingly, the first and second gap layers are constructed as thin as possible without shorting the first and second shield layers to the read sensor and the first and second lead layers. The read sensor has first and second side edges that define a track width of the read head. The narrower the track width the higher the track density in terms of tracks per inch read by the read head. The product of the linear density and the track density equals the areal density of the read head which is the bit reading capability of the read head per square inch of the magnetic media.
The first and second lead layers abut the first and second side edges of the read sensor in a connection which is referred to in the art as a contiguous junction. Each of the read sensor and the lead layers comprises a plurality of films. A spin valve read sensor typically comprises a spacer layer sandwiched between a free layer and a pinned layer. Adjacent the pinned layer is a pinning layer for pinning a magnetic moment of the pinned layer. The free layer has a magnetic moment that is free to rotate relative to the fixed magnetic moment of the pinned layer in response to field incursions from the rotating magnetic disk which causes a change in resistance of the read sensor to the sense current that can be detected as potential changes by processing circuitry. Each lead layer typically comprises one or more films that longitudinally bias the free layer of the read sensor, and an electrically conductive film sandwiched between an adhesion layer and a cap layer.
The free layer is a soft ferromagnetic material, such as Permalloy (Ni--Fe), that is deposited in the presence of a magnetic field that orients the magnetic spins of the free layer substantially parallel to the ABS. Accordingly, the magnetic moment of the free layer is set along what is referred to in the art as an easy axis. Magnetic incursions from the rotating magnetic disk rotate the magnetic moment of the free layer from the easy axis. Typically, magnetic spins of the free layer are unstable when subjected to a magnetic field. These magnetic spins are in domains that interface with each other along domain walls. When the free layer is subjected to and then released from the magnetic field, the domain walls do not return to their original orientation. This changes the magnetics of the free layer and affects its performance. Accordingly, the free layer must be stabilized by longitudinal biasing so that the magnetic spins of the free layer are directed parallel to the ABS in a single domain state.
There are two stabilization schemes for longitudinally biasing the free layer. One stabilization scheme is to provide each of the lead layers with a non-magnetic seed layer and a hard magnetic film that magnetostatically interacts with the free layer along its easy axis. The other stabilization scheme is to provide each of the lead layers with a soft ferromagnetic film and an antiferromagnetic metallic film that exchange couple to each other, resulting in magnetostatic and exchange interactions with the free layer along the easy axis. Each stabilization scheme has its advantages and disadvantages. A read sensor with the antiferromagnetic stabilization scheme has a better read sensitivity than that with the hard magnetic stabilization scheme. However, the antiferromagnetic film is typically thicker than the hard magnetic film which causes a greater step between the read sensor and each of the first and second lead layers. This greater step requires that the second read gap layer be thicker in order to ensure that there are no pinholes between the lead layers and the second shield layer that can cause a short in the sense current circuit. A thicker second read gap layer equates to less linear read density of the read head. Accordingly, there is a strong need to provide a read head that has a high read sensitivity similar to a read head with an antiferromagnetic stabilization scheme and yet has a small step similar to a read head with a hard magnetic film stabilization scheme.